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1
Balevi, Birtan Taner. "Flutter Analysis And Simulated Flutter Test Of Wings." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12615016/index.pdf.
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Flutter is a dynamic instability which can result in catastrophic failures of an air vehicle. Preventing flutter can be an important factor in the aircraft design, affecting the structural design. Thus, the weight and performance of the aircraft is also being affected. Understanding the role of each design factor of a wing on the onset of flutter can help designers on the flutter clearance of the aircraft. Analysis to predict flutter, ground vibration tests and flight flutter tests, which are performed to verify that the dedicated flight envelope is clear from flutter, are the most important certification processes in modern aviation.
Flight flutter testing is a very expensive process. In flight flutter tests the air vehicle is instrumentated with exciters, accelerometers and transmitters to send the test data simultaneously to the ground station to be analyzed. Since flutter is a very severe instability, which develops suddenly, the data should be followed carefully by the engineers at the ground station and feedback should be provided to the pilot urgently when needed. Low test step numbers per flight, increases the cost of flutter testing. Increasing efforts in pre-flight test processes in flutter prediction may narrow the flight flutter test steps and decrease the costs.
In this study, flutter prediction methods are investigated to aid the flutter test process. For incompressible flight conditions, some sample problems are solved using typical section model. Flutter solutions of a simple 3D wing are also performed via a coupled finite element linear aerodynamics approach using the commercial tool Nastran. 3D flutter solutions of the wing are compared with the typical section solutions to see how close can the typical section method predict flutter compared to the flutter analyis using the three dimensional wing model. A simulated flutter test method is introduced utilizing the two dimensional typical section method. It is shown that with a simple two dimensional typical section method, flutter test simulation can be performed successfully as long as the typical section model approximates the dynamic properties of the wing closely.
2
Khalak, Asif 1972. "Parametric dependencies of aeroengine flutter for flutter clearance applications." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/8818.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2000."September 2000."
Includes bibliographical references (p. 223-228).
This thesis describes the effects of operational parameters upon aeroengine flutter stability. The study is composed of three parts: theoretical development of relevant parameters, exploration of a computational model, and analysis of fully scaled test data. Results from these studies are used to develop a rational flutter clearance methodology-a test procedure to ensure flutter-free operation. It is shown, under conditions relevant to aeroengines, that four nondimensional parameters are necessary and sufficient for flutter stability assessment of a given rotor geometry. We introduce a new parameter, termed the reduced damping, g/p *, which collapses the combined effects of mechanical damping and mass ratio (blade mass to fluid inertia). Furthermore, the introduction of the compressible reduced frequency, K*, makes it possible to uniquely separate the corrected performance map from the non-dimensional operating environment (including inlet temperature and pressure). Simultaneous plots of the performance map of corrected mass flow and corrected speed, (^.mc, Nc), with the (K*, g/p*) map provide a dimensionally complete and fully integrated view of flutter stability, as demonstrated in the context of a historic multimission engine. A parametric, computational study was conducted using a 2D, linearized unsteady, compressible, potential flow model of a vibrating cascade. This study showed the independent effects of Mach number, inlet flow angle, and reduced frequency upon flutter stability in terms of critical reduced damping, which corroborates the 4D view of flutter stability. Test data from a full-scale transonic fan, spanning the full 4D parameter space, were also analyzed. A novel boundary fitting tool was developed for data processing, which can handle the generic case of sparse, multidimensional, binary data. The results indicate that the inlet pressure does not alone determine the flight condition effects upon flutter, which necessitates the use of the complete 4D parameter set. Such a complete view of the flutter boundary is constructed, and sensitivities with respect to various parameters are estimated. A rational flutter clearance procedure is proposed. Trends in K* and g/p* allow one to rapidly determine the worst-cases for testing a given design. One may also use sensitivities to extend the results of sea level static (SLS) testing, if the worst case is relatively close to the SLS condition.
by Asif Khalak.
Ph.D.
3
Barman, Emelie. "Aerodynamics of Flutter." Thesis, KTH, Mekanik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-34152.
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The unsteady ow around an aerofoil placed in a uniform ow stream with an angle of attack is investigated, under the assumption of inviscid, incompressible, two-dimensional flow. In particular, a function of the velocity jump over the wake is achieved, where this function depends on the horizontal displacement and time. The aerofoil geometry is represented by two arbitrary functions, one for the upper and one for the lower side of the aerofoil. These functions are dependent on time, hence the aerofoil can perform oscillating movement, which is the case when subjected to utter. The governing equations for the ow are the Euler equations. By assuming thin aerofoil, small angle of attack and that the perturbation of the wake is small, the problem is linearised. It is shown that the linearised Euler equations can be rewritten as the Cauchy-Riemann equations, and an analytic function exists where its real part is the horizontal velocity component and its imaginary part is the vertical velocity component with opposite sign. The ow eld is then investigated in the complex plane by making an appropriate branch cut removing all discontinuities, and with restrictions on the analytic function such that the kinematic and boundary conditions are satis ed. By using Cauchy's integral formula an expression for the anti-symmetric part of the analytic function is achieved. A general expression for the velocity jump over the wake is obtained, which is applied to the speci c case of harmonic oscillations for a symmetric aerofoil. In the end three types of utter is investigated; twisting oscillations around the centre of stiness, vertical oscillation, and aileron flutter.
4
Zhao, Fanzhou. "Embedded blade row flutter." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/51151.
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Modern gas turbine design continues to drive towards improved performance, reduced weight and reduced cost. This trend of aero-engine design results in thinned blade aerofoils which are more prone to aeroelastic problems such as flutter. Whilst extensive work has been conducted to study the flutter of isolated turbomachinery blades, the number of research concerning the unsteady interactions between the blade vibration, the resulting acoustic reflections and flutter is very limited. In this thesis, the flutter of such embedded blade rows is studied to gain understanding as for why and how such interactions can result in flutter. It is shown that this type of flutter instability can occur for single stage fan blades and multi-stage core compressors. Unsteady CFD computations are carried out to study the influence of acoustic reflections from the intake on flutter of a fan blade. It is shown that the accurate prediction of flutter boundary for a fan blade requires modelling of the intake. Different intakes can produce different flutter boundaries for the same fan blade and the resulting flutter boundary is a function of the intake geometry in front of it. The above finding, which has also been demonstrated experimentally, is a result of acoustic reflections from the intake. Through in-depth post-processing of the results obtained from wave-splitting of the unsteady CFD solutions, the relationship between the phase and amplitude of the reflected acoustic waves and flutter stability of the blade is established. By using an analytical approach to calculate the propagation and reflection of acoustic waves in the intake, a novel low- fidelity model capable of evaluating the susceptibility of a fan blade to flutter is proposed. The proposed model works in a similar fashion to the Campbell diagram, which allows one to identify the region (in compressor map) where flutter is likely to occur at early design stages of an engine. In the second part of this thesis, the influence of acoustic reflections from adjacent blade rows on flutter stability of an embedded rotor in a multi-stage compressor is studied using unsteady CFD computations. It is shown that reflections of acoustic waves, generated by the rotor blade vibration, from the adjacent blade rows have a significant impact on the flutter stability of the embedded rotor, and the computations using the isolated rotor can lead to significant over-optimistic predictions of the flutter boundary. Based on the understanding gained, an alternative strategy, aiming to reduce the computational cost, for the flutter analysis of such embedded blades is proposed. The method works by modelling the propagation and reflection of acoustic waves at the adjacent blade rows using an analytical method, whereby flutter computations of the embedded rotor can be performed in an isolated fashion by imposing the calculated reflected waves as unsteady plane sources. Computations using the proposed model can lead to two orders of magnitude reduction in computational cost compared with time domain full annulus multi-row computations. The computed results using the developed low-fidelity model show good correlation with the results obtained using full annulus multi-row models.
5
Dong, Bonian. "Numerical simulation of wakes, blade-vortex interaction, flutter, and flutter suppression by feedback control." Diss., This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-07282008-134810/.
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Chernysheva, Olga V. "Flutter in sectored turbine vanes." Doctoral thesis, KTH, Energy Technology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3737.
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In order to eliminate or reduce vibration problems inturbomachines without a high increase in the complexity of thevibratory behavior, the adjacent airfoils around the wheel areoften mechanically connected together with lacing wires, tip orpart-span shrouds in a number of identical sectors. Although anaerodynamic stabilizing effect of tying airfoils together ingroups on the whole cascade is indicated by numerical andexperimental studies, for some operating conditions suchsectored vane cascade can still remain unstable.
The goal of the present work is to investigate thepossibilities of a sectored vane cascade to undergoself-excited vibrations or flutter. The presented method forpredicting the aerodynamic response of a sectored vane cascadeis based on the aerodynamic work influence coefficientrepresentation of freestanding blade cascade. The sectored vaneanalysis assumes that the vibration frequency is the same forall blades in the sectored vane, while the vibration amplitudesand mode shapes can be different for each individual blade inthe sector. Additionally, the vibration frequency as well asthe amplitudes and mode shapes are supposed to be known.
The aerodynamic analysis of freestanding blade cascade isperformed with twodimensional inviscid linearized flow model.As far as feasible the study is supported by non-linear flowmodel analysis as well as by performing comparisons againstavailable experimental data in order to minimize theuncertainties of the numerical modeling on the physicalconclusions of the study.
As has been shown for the freestanding low-pressure turbineblade, the blade mode shape gives an important contributioninto the aerodynamic stability of the cascade. During thepreliminary design, it has been recommended to take intoaccount the mode shape as well rather than only reducedfrequency. In the present work further investigation using foursignificantly different turbine geometries makes these findingsmore general, independent from the low-pressure turbine bladegeometry. The investigation also continues towards a sectoredvane cascade. A parametrical analysis summarizing the effect ofthe reduced frequency and real sector mode shape is carried outfor a low-pressure sectored vane cascade for differentvibration amplitude distributions between the airfoils in thesector as well as different numbers of the airfoils in thesector. Critical (towards flutter) reduced frequency maps areprovided for torsion- and bending-dominated sectored vane modeshapes. Utilizing such maps at the early design stages helps toimprove the aerodynamic stability of low-pressure sectoredvanes.
A special emphasis in the present work is put on theimportance for the chosen unsteady inviscid flow model to bewell-posed during numerical calculations. The necessity for thecorrect simulation of the far-field boundary conditions indefining the stability margin of the blade rows isdemonstrated. Existing and new-developed boundary conditionsare described. It is shown that the result of numerical flowcalculations is dependent more on the quality of boundaryconditions, and less on the physical extension of thecomputational domain. Keywords: Turbomachinery, Aerodynamics,Unsteady CFD, Design, Flutter, Low-Pressure Turbine, Blade ModeShape, Critical Reduced Frequency, Sectored Vane Mode Shape,Vibration Amplitude Distribution, Far-field 2D Non-ReflectingBoundary Conditions. omain.
Keywords:Turbomachinery, Aerodynamics, Unsteady CFD,Design, Flutter, Low-Pressure Turbine, Blade Mode Shape,Critical Reduced Frequency, Sectored Vane Mode Shape, VibrationAmplitude Distribution, Far-field 2D Non-Reflecting BoundaryConditions.
7
Akbari, Mohammad Hadi. "Flutter evaluation of an airfoil." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=69529.
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The problem of flutter is first introduced. The equations of motion of an airfoil with two degrees of freedom, in pitch and plunge, are obtained. Then, the unsteady aerodynamic theories for different flow regimes are presented. The traditional solutions to the flutter problem, namely, the p-k and U-g methods, are formulated, and the Laplace transformation method for flutter analysis is also introduced. Then, the effect of different design parameters of an airfoil on the flutter speed is analyzed, both in the incompressible and transonic regimes. Furthermore, the effect of the relative values of the design parameters on the occurrence of flutter is investigated. Finally, some general conclusions regarding the above-mentioned phenomena are derived. The goal of this work is the fact that, the unsteady aerodynamic data has been used, both in the incompressible and transonic regimes, and, therefore, the obtained results are fairly precise.
8
Shao, Lin, and 邵琳. "Flutter of a cantilevered plate." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B4559031X.
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Duchesne, Laurent Guillaume. "Advanced techniques for flutter clearance." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/49966.
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Perrocheau, Mathilde. "Flutter Prediction in Transonic Regime." Thesis, KTH, Flygdynamik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-234840.
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The flutter is a dangerous aeroelastic instability that can cause dramatic failures. It is important to evaluate in which conditions it can occur to ensure the safety of the pilots and the passengers. As flight tests are very expensive and hazardous, the need for efficient and trustworthy numerical tools becomes essential. This report focuses on two methods to predict the flutter conditions in the transonic domain. To evaluate the accuracy of these tools, their results are compared to experimental data gathered during a wind-tunnel test. The influence of the Mach number and the angle of attack on the flutter conditions is studied and physical explanations are put forward.
11
Anselme, Frédéric. "L'ablation du flutter auriculaire typique." Rouen, 2000. http://www.theses.fr/2000ROUEA009.
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Grâce au développement des techniques de cartographie et d'imagerie, le circuit du flutter auriculaire typique a été parfaitement déterminé, ce qui a contribué à l'essor de son traitement curatif par ablation. Dans ce travail, nous avons tenté de répondre à certaines questions d'ordre physiopathologiques, technique, et clinique concernant cette arythmie et son traitement. Ainsi, nous avons montré 1 ) que la localisation du bloc de conduction unidirectionnel nécessaire à l'induction d'une réentrée et du flutter, se situe au niveau de l'isthme cavo-tricuspidien, siège également de la zone de conduction lente; 2) l'absence de bénéfice à utiliser une électrode de 8 mm à simple thermocouple par rapport à une éléctrode standard de 4 mm dans l'ablation du flutter auriculaire typique; 3) que l'ablation du flutter réalisée au niveau de la partie postérieure de l'isthme est aussi efficace que celle effectuée au niveau de la partie antérieure de l'isthme, mais est associée à un risque de troubles conductifs auricolo-ventriculaires; 4) que l'obtention d'un bloc isthmique complet bidirectionnel, documenté par la cartographie d'activaton, est un critère prédictif de succès de l'ablation à très long terme, qui se traduit par une amélioration durable de l'état fonctionnel et de la qualité de vie. Les palpitations présentées par les patients aprsè ablation sont dues à la survenue d'accès de fibrilation auriculaire; 5) que la technique d'analyse des potentiels auriculaires sur la ligne d'ablation est capable de déterminer la présence d'un bloc isthmique complet bidirectionnel, mais est plus difficile d'utilisation que la technique "classique" de cartographie d'activation. L'utilisation concomitante de ces 2 techniques, couplée à la stimulation positionelle en présence d'un aspect de bloc isthmique horaire incomplet, est préconisée dans l'évaluation des propriétés de conduction de l'isthme cavo-tricuspiden au cours de l'ablation du flutter auriculaire typiqueOver the past decade, the continuous improvement of intra-cardiac mapping techniques, contributed to a better understanding of the typical atrial flutter circuit. Arrhythmia recurrences are now prevented by the creation of a radiofrequency linear lesion at the inferior vena cava - tricuspid annulus isthmus. In this work, we aimed at answering to several pathophysiological, technical and clinical issues regarding this arrhythmia and its ablation by catheter. We have demonstrated that 1) initiation of typical atrial flutter is associated with appearance of functional unidirectional block at the inferior vena cava - tricuspid annulus isthmus; 2) there is no particular advantage of using a 8 mm single thermocouple electrode as compared to a regular 4 mm electrode in atrial flutter ablation; 3) although atrial flutter ablation is equally effective at the posterior and anterior isthmus, success seems easier to obtain when the anterior isthmus is first targeted. Ablation at the posterior isthmus is associated with a significant risk of AV block; 4) palpitations after creation of complete bidirectional isthmus block are due mostly to atrial fibrillation but not to atrial flutter recurrence. This technique provides a significant and persistent clinical benefit and may suppress all atrial arrhytmia in a subset of patient suffering from both atrial flutter and fibrillation ; 5) although feasible, the on-site atrial potential analysis appears inferior to the classical activation mapping technique, mainly because of the ambiguity of electrogram interpretation along the ablation line. When combined with the activation mapping technique, on-site atrial potential analysis brings additional information regarding isthmus conduction properties. Therefore, optimally both methods should be used concomitantly
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Tarbet, Robin M. (Robin Michael) Carleton University Dissertation Engineering Aeronautical. "Techniques for examining nonlinear flutter." Ottawa, 1990.
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Turner, Mark A. "A computational investigation of wake-induced airfoil flutter in incompressible flow and active flutter control." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA281534.
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Ashawesh, Gamal Mohamed. "Flutter behaviour of composite aircraft wings." Thesis, Cranfield University, 1999. http://hdl.handle.net/1826/3900.
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This research work presents series of investigations into the structural
dynamics and dynamic aeroelastic (flutter) behaviour of composite and metal wings.
The study begins with a literature review where the development and an over view of
the previous investigations in this field are presented. Static stiffness is very important
to any type of analysis, especially in both dynamic and flutter analysis as in this case.
Therefore, different methods are presented and used for the determination of cross-
sectional rigidities such as bending, torsional and bending-torsional coupling rigidities
properties for beams constructed of laminated and thin-walled structures materials.
A free vibration experimental analysis was conducted on the physical
Cranfield Al aerobatic composite wing box structure. The composite wing box was
exited in the frequency range of 0 to 300 Hz, with both sinusoidal and random
excitations, which yields to six resonant frequencies.
The theoretical free vibration and flutter analysis was then carried out firstly
on the physical Cranfield Al aerobatic metal wing box. The metal wing was modeled
using two techniques; the first model was a simplified wing structure (beam with
lumped mass). This analysis of the simplified model was done using CALFUN
program for the free vibration analysis and using MSC/NASTRAN for both free
vibration and flutter analysis. The second model was a detailed model created by
MSC/PATRAN and analyzed by MSC/NASTRAN for the free vibration and flutter
analysis. The obtained results (natural frequencies and mode shapes) showed a good
agreement between the simplified, detailed model and the experimental test. It was
found that even with using the simplified model, but having the physical
characteristics of the wing leads to a good agreement with the detailed model and
experimental work. This also showed the importance of simplified model at early
stage of the design to the structural designer in terms of the accuracy, time, and size of
the model.
Free vibration and flutter analysis was carried out on the Cranfield Al
aerobatic composite wing box with the original laminate lay ups using Lanczos
method for extracting the eigenvalues and eigenvectors and using PK method for
finding the flutter speed and frequency provided by MSC/NASTRAN. The results were compared with the experimental vibration analysis and were found a large
difference in the first frequency mode. To investigate the cause of the variation, a
series of static loading tests were performed on the composite wing box. Also a
comparison of the results between the metal and composite aerobatic wing box is
presented. It was found that the large difference could be due to the combination of
different parameters such as stiffness (age of the wing, delamination and boundary
condition), and increase of mass of the physical wing box (due to environmental effect
such as moisture) and modelling differences.
The free vibration characteristics of ten wing models constructed from
balanced and unbalanced laminate configurations were carried out using Lanczos
method provided by MSC/NASTRAN. The analysis was done on ten wing models
modeled to simulate Circumferentially Asymmetric Stiffness (CAS) and
Circumferentially Uniform Stiffness (CUS). The static equivalent stiffness was
calculated using two different modeling methods for a wide range of fibre angles 0 (-
90° to 90°) of the skins. The variations and the importance of the stiffness ratio
(EI/GJ), parameter (K/GJ), and the frequency ratio (wb/(Ot) are illustrated against the
fibre angle 0. It was found that the fundamental bending frequency is slightly lower in
the case of CUS (K = 0) as compared to the CAS (K # 0), which was not the case in
the plate model. Also, the first torsion frequency mode in the case of CUS was much
lower than the first torsion frequency of the CAS, which was not the case of the plate
model. However, the effect of bend-twist coupling stiffness on the mode shapes was
pronounced in both structures especially at the area of higher coupling stiffness.
The flutter analysis was done using the PK method for all the wing models of
both (CAS) and (CUS) configurations. The results showed the optimum value of
flutter speed and the importance of the stiffness ratio (EI/GJ), parameter (K/GJ), the
frequency ratio (wb/wt), which will lead to the maximum flutter speed. The effects of
the above parameters, geometrical coupling and the wash-in and washout on the non-
dimensional flutter speed are presented. It was concluded that, negative bend-twist
coupling stiffness is beneficial for flutter speed compared to the positive bend-twist
coupling stiffness at 00<0<_30°. It was also found that the flutter speed for the CUS
was higher at 00<0<_300 compared to the CAS. Also creating an offsite between the elastic axis and center of gravity (behind) decreases the flutter speed whereas having
more ribs increases the flutter speed compared with adding stringers.
The analysis was carried out on a more practical composite wing box, which
was the physical Cranfield Al aerobatic composite wing box. There are some
simplifications on the physical structure, which are the cancellation of the woven
materials and keeping the same laminate lay ups for the upper and lower skin. The
natural frequency and mode shapes was obtained and plotted against the fibre angle 0
of the upper and lower skin for the (CAS) and (CUS) configurations using both
symmetric and asymmetric laminate for the upper and lower skin. The flutter analysis
was done for the composite wing box for the same configurations as in the free
vibration analysis. The effects of the fibre angle 0 of the upper and lower skin,
material coupling stiffness, wash-in and wash-out, and structural damping on the non-
dimensional flutter speed and flutter frequencies are illustrated. It was found that in
this configurations both structural and bend-twist coupling are exist, negative bend-
twist coupling (wash-in) increases the flutter speed compared with the positive bend-
twist coupling, and the possibility of increasing the flutter speed at higher frequency
ratio, structural coupling and positive bend-twist coupling (wash-out).
15
Perry, Brendan. "Predictions of flutter at transonic speeds." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.498853.
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Abbasi, Asim Ali. "Advances in flight flutter testing techniques." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493963.
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Flight flutter testing is a mandatory test performed to demonstrate that prototype aircraft are free from flutter - a violent destructive vibration. Flight flutter testing techniques have advanced a great deal over the last 50 years but the process is still risky, time consuming and costly. Therefore, the demand for reduction in time and cost of the flight test procedure and development of efficient online flutter prediction tools among other related issues is ever-growing. This research has dealt with two of the key issues and the methods developed have been validated successfully on simulated aeroelastic data sets corrupted with various levels and types of noise.
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Forhad, Md Moinul Islam. "Robustness analysis for turbomachinery stall flutter." Master's thesis, University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4894.
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As compared with other robustness analysis tools, such as Hsubscript inf], the Mu analysis is less conservative and can handle both structured and unstructured perturbations. Finally, Genetic Algorithm is used as an optimization tool to find ideal parameters that will ensure best performance in terms of damping out flutter. Simulation results show that the procedure described in this thesis can be effective in studying the flutter stability margin and can be used to guide the gas turbine blade design.; Flutter is an aeroelastic instability phenomenon that can result either in serious damage or complete destruction of a gas turbine blade structure due to high cycle fatigue. Although 90% of potential high cycle fatigue occurrences are uncovered during engine development, the remaining 10% stand for one third of the total engine development costs. Field experience has shown that during the last decades as much as 46% of fighter aircrafts were not mission-capable in certain periods due to high cycle fatigue related mishaps. To assure a reliable and safe operation, potential for blade flutter must be eliminated from the turbomachinery stages. However, even the most computationally intensive higher order models of today are not able to predict flutter accurately. Moreover, there are uncertainties in the operational environment, and gas turbine parts degrade over time due to fouling, erosion and corrosion resulting in parametric uncertainties. Therefore, it is essential to design engines that are robust with respect to the possible uncertainties. In this thesis, the robustness of an axial compressor blade design is studied with respect to parametric uncertainties through the Mu analysis. The nominal flutter model is adopted from (9). This model was derived by matching a two dimensional incompressible flow field across the flexible rotor and the rigid stator. The aerodynamic load on the blade is derived via the control volume analysis. For use in the Mu analysis, first the model originally described by a set of partial differential equations is reduced to ordinary differential equations by the Fourier series based collocation method. After that, the nominal model is obtained by linearizing the achieved non-linear ordinary differential equations. The uncertainties coming from the modeling assumptions and imperfectly known parameters and coefficients are all modeled as parametric uncertainties through the Monte Carlo simulation.ID: 030423207; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (M.S.)--University of Central Florida, 2011.; Includes bibliographical references (p. 44-47).
M.S.
Masters
Mechanical, Materials, and Aerospace Engineering
Engineering and Computer Science
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Turevskiy, Arkadiy 1974. "Flutter boundary prediction using experimental data." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/50327.
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Bidinotto, Jorge Henrique. "Detecção de \"flutter\" por imageamento infravermelho." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/18/18148/tde-21072016-095118/.
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O crescente desempenho das aeronaves aliado ao desenvolvimento de materiais cada vez mais leves e flexíveis tem levado os projetistas a utilizar coeficientes de segurança estruturais cada vez menores, o que pode tornar as superfícies aerodinâmicas mais susceptíveis a fenômenos aeroelásticos, entre eles o flutter, que deve ser cuidadosamente investigado com ensaios em solo e em voo durante o desenvolvimento e certificação de aeronaves. Para tais ensaios, é importante uma instrumentação adequada, que possa prever o aparecimento de vibrações indesejadas e possa agir de forma menos intrusiva possível, de forma a não modificar o comportamento dinâmico do sistema. Esse trabalho propõe o uso do imageamento infravermelho como instrumento para detecção de flutter, analisando se essa técnica é adequada para tal aplicação e quais as vantagens e desvantagens de seu uso. Para isso é feita uma revisão da literatura pertinente, apresentando conceitos de flutter, mecânica estrutural e tecnologia infravermelho, e em seguida é apresentada uma estrutura conhecida para se testar a técnica referida. São realizados simulações e testes na estrutura para levantamento das suas características e finalmente testes em túnel de vento, onde se verifica o funcionamento desta técnica, seus pontos positivos e pontos que requerem melhorias.The increasing performance of aircraft together with the development of increasingly lightweight and flexible materials has led designers to use smaller structural safety factors, which can make the aerodynamic surfaces more susceptible to aeroelastic phenomena, including flutter, which should be carefully investigated with ground and flight tests during the aircraft development and certification. For such assays, it is important to use proper instrumentation, which can predict the occurrence of unwanted vibrations to act in less intrusive way possible, in order to not modify the system dynamic behavior. This work proposes the use of infrared imaging as a tool for detection of flutter, analyzing whether this technique is suitable for such application, the advantages and disadvantages of their use. For this, a review of the relevant literature is made, presenting flutter concepts, structural mechanics and infrared technology, and then a known structure used to test the technique is presented. Simulations and tests to survey the structure characteristics are presented as well as tests in the wind tunnel, performing the operation of this technique in order to address its positive points and areas that needs improvement.
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Resende, Hugo Borelli. "Estudos na análise de whirl flutter." Instituto Tecnológico de Aeronáutica, 1987. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=1536.
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O whirl flutter, em se tratando de uma instabilidade que pode ocorrer durante o vôo de uma aeronave e levar a uma condição de falha estrutural, deve ser devidamente estudado durante o projeto de uma aeronave moderna de modo a manter manter um nível de segurança adequada, mesmo porque o processo de homologação final inclui requesitos sobre a ocorrência do fenômeno. Assim, para uma empresa aeronáutica é essencial que exista um programa numérico acessível que permita este tipo de análise para o caso de configurações as mais gerais possíveis. Este estudo visou exatamente a implementação de um programa assim, tendo sido utilizado um modelo em que o motor é considerado um corpo rígido apoiado elasticamente em uma estrutura de suporte, a qual não necessariamente é rígida. A extensão para mais de um corpo é imediata, considerando-se, então, que os corpos estão ligados elasticamente entre si. Todos os seis graus de liberdade dos centros de gravidade de cada corpo são mantidos. Com relação aos esforços aerodinâmicos, são utilizados resultados convencionais para hélices de pás rígidas, mas procurou-se mostrar um caminho através do qual fosse possível a utilização de uma teoria de superfície de sustentação para o cálculo aerodinâmico. Finalizando, foram feitas comparações com resultados anteriores, além de se procurar verificar as diferenças de comportamento das fronteiras de estabilidade entre os modelos com graus de complexidade distintos, especialmente entre modelos de dois e seis graus de liberdade.
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Bååthe, Axel. "Transonic Flutter for aGeneric Fighter Configuration." Thesis, KTH, Flygdynamik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-233884.
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A hazardous and not fully understood aeroelastic phenomenon is the transonic dip,the decrease in flutter dynamic pressure that occurs for most aircraft configurationsin transonic flows. The difficulty of predicting this phenomenon forces aircraft manufacturersto run long and costly flight test campaigns to demonstrate flutter-free behaviourof their aircraft at transonic Mach numbers.In this project, subsonic and transonic flutter calculations for the KTH-NASA genericfighter research model have been performed and compared to existing experimentalflutter data from wind tunnel tests performed at NASA Langley in 2016. For the fluttercalculations, industry-standard linear panel methods have been used together with afinite element model from NASTRAN.Further, an alternative approach for more accurate transonic flutter predictions usingthe full-potential solver Phi has been investigated. To predict flutter using this newmethodology a simplified structural model has been used together with aerodynamicmeshes of the main wing. The purpose of the approach was to see if it was possibleto find a method that was more accurate than panel methods in the transonic regimewhilst still being suitable for use during iterative design processes.The results of this project demonstrated that industry-standard linear panel methodssignificantly over-predict the flutter boundary in the transonic regime. It was alsoseen that the flutter predictions using Phi showed potential, being close to the linearresults for the same configuration as tested in Phi. For improved transonic accuracy inPhi, an improved transonic flow finite element formulation could possibly help .Another challenge with Phi is the requirement of an explicit wake from all liftingsurfaces in the aerodynamic mesh. Therefore, a method for meshing external storeswith blunt trailing edges needs to be developed. One concept suggested in this projectis to model external stores in "2.5D", representing external stores using airfoils withsharp trailing edges.Ett farligt och inte helt utrett aeroelastiskt fenomen är den transoniska dippen, minskningeni dynamiska trycket vid fladder som inträffar för de flesta flygplan i transoniskaflöden. Svårigheten i att prediktera detta fenomen tvingar flygplanstillverkare attbedriva tidskrävande och kostsam flygprovsverksamhet för att demonstrera att derasflygplan ej uppvisar fladderbeteende i transonik inom det tilltänkta användningsområdet.I detta projekt har fladderberäkningar genomförts i både underljud och transonikför en generisk stridsflygplansmodell i skala 1:4 ämnad för forskning, byggd som ettsamarbete mellan KTH och NASA. Beräkningarna har också jämförts med fladderresultatfrån vindtunnelprov genomförda vid NASA Langley under sommaren 2016. Förfladderberäkningarna har industri-standarden linjära panelmetoder används tillsammansmed en befintlig finit element modell för användning i NASTRAN.Vidare har ett alternativt tillvägagångssätt för att förbättra precisionen i transoniskafladderresultat genom att använda potentiallösaren Phi undersökts. En förenkladstrukturmodell har använts tillsammans med aerodynamiska nät av huvudvingen föratt prediktera fladder. Syftet med denna metodik var att undersöka om det var möjligtatt hitta en metod som i transoniska flöden var mer exakt än panelmetoder men somfortfarande kunde användas i iterativa design processer.Resultaten från detta projekt visade att linjära panelmetoder, som de som används iindustrin, är signifikant icke-konservativa gällande fladdergränsen i transonik. Resultatenfrån Phi visade potential genom att vara nära de linjära resultaten som räknadesfram med hjälp av panelmetoder för samma konfiguration som i Phi. För ökad transonisknoggrannhet i Phi kan möjligen en förbättrad transonisk element-formuleringhjälpa.En annan utmaning med Phi är kravet på en explicit vak från alla bärande ytor idet aerodynamiska nätet. Därför behöver det utvecklas en metodik för nätgenereringav yttre laster med trubbiga bakkanter. Ett koncept som föreslås i denna rapport är attmodellera yttre laster i "2.5D", där alla yttre laster beskrivs genom att använda vingprofilermed skarpa bakkanter.
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Costa, Tiago Francisco Gomes da. "Estudo numérico de uma asa com controle ativo de flutter por realimentação da pressão medida num ponto." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/18/18148/tde-27112007-001723/.
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Neste trabalho é desenvolvido um sistema de controle ativo para supressão de flutter de uma asa utilizando-se sensores de pressão em pontos estratégicos de sua superfície. O flutter é um fenômeno aeroelástico que caracteriza um acoplamento instável entre estrutura flexível e escoamento aerodinâmico não estacionário. Quando a modificação da estrutura ou da aerodinâmica da asa não é viável, o uso de sistemas de controle passa a ser uma boa opção. Para o desenvolvimento do sistema de controle proposto, é primeiramente desenvolvido um modelo numérico de asa flexível. Com esse modelo numérico e a pressão na superfície da asa medida em certos pontos e realimentada ao sistema controlador, são determinadas correções no ângulo de uma superfície de controle no bordo de fuga. A tentativa de se utilizar um sistema de controle bem simples, com o uso de um único sensor de pressão, mostra a viabilidade de se implementar um sistema deste tipo em aeronaves reais. Esse sistema pode tornar-se uma alternativa aos desenvolvidos até então com o uso de acelerômetros, além de ser útil em sistemas onde se procura prever o estol e observar o comportamento da distribuição de pressão sobre a asa em vôo.In this work, a wing flutter suppression active control system using pressure sensors in strategic points is developed. Flutter is an aeroelastic phenomenon characterized by an unstable coupling of a flexible structure and a non-stationary aerodynamic flow. When changes of the wing structure or of the aerodynamics are not viable, the use of automatic control systems becomes a good option. For the developing of the suggested control system, a numeric model of a finite flexible wing is firstly done. With this model and the pressure over the wing surface read in certain points and fedback to the control system, changes of the control surface angle on the trailing edge are determined. The attempt to use a simple control system, with a unique pressure sensor shows the viability of implanting this kind of system in real aircrafts. This system may become an alternative to those developed until now, using accelerometers. Yet, it could be useful, in systems where it is necessary to predict stall and observe the pressure load behavior over the wing in flight.
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Kakkavas, Constantinos. "Computational investigation of subsonic torsional airfoil flutter." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1998. http://handle.dtic.mil/100.2/ADA359731.
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Thesis (M.S. in Aeronautical Engineering) Naval Postgraduate School, December 1998."December 1998." Thesis advisor(s): Max F. Platzer, Kevin D. Jones. Includes bibliographical references (p. 89-90). Also available online.
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Karadal, Fatih Mutlu. "Active Flutter Suppression Of A Smart Fin." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609830/index.pdf.
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This study presents the theoretical analysis of an active flutter suppression methodology applied to a smart fin. The smart fin consists of a cantilever aluminum plate-like structure with surface bonded piezoelectric (PZT, Lead- Zirconate-Titanate) patches.
A thermal analogy method for the purpose of modeling of piezoelectric actuators in MSC®/NASTRAN based on the analogy between thermal strains and piezoelectric strains was presented. The results obtained by the thermal analogy were compared with the reference results and very good agreement was observed. The unsteady aerodynamic loads acting on the structure were calculated by using a linear two-dimensional Doublet-Lattice Method available in MSC®
/NASTRAN. These aerodynamic loads were approximated as rational functions of the Laplace variable by using one of the aerodynamic approximation schemes, Roger&
#8217
s approximation, with least-squares method. These approximated aerodynamic loads together with the structural matrices obtained by the finite element method were used to develop the aeroelastic equations of motion of the smart fin in state-space form. The Hinf robust controllers were then designed for the state-space aeroelastic model of the smart fin by considering both SISO (Single-Input Single-Output) and MIMO (Multi-Input Multi-Output) system models. The verification studies of the controllers showed satisfactory flutter suppression performance around the flutter point and a significant improvement in the flutter speed of the smart fin was also observed.
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Clarkson, Jeffrey Dow. "A computational investigation of airfoil stall flutter." Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/23579.
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Lee, Sung-yeoul. "Viscous effects in predicting transonic flutter boundary." Thesis, Cranfield University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393619.
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Phibel, Richard. "A numerical investigation of labyrinth seal flutter." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/59973.
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This thesis investigates numerically the phenomenon of flutter in labyrinth seals. Computational fluid dynamics (CFD) methods are used to predict the fluid forces produced in the labyrinth when one of the seal members is vibrating in its natural mode. The geometry of the seal, the vibrational characteristics and the flow characteristics are varied to determine their influence on the aeroelastic stability. The CFD results are used to develop a bulk-flow model for labyrinth seal flutter analysis. An aeroelastic design procedure for labyrinth seal is pro-posed.
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Pons, Arion Douglas. "Aeroelastic flutter as a multiparameter eigenvalue problem." Thesis, University of Canterbury. Department of Mechanical Engineering, 2015. http://hdl.handle.net/10092/11265.
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In this thesis we explore the relationship between aeroelastic flutter and multiparameter spectral theory. We first introduce the basic concept of the relationship between these two fields in abstract terms. Then we expand on this initial concept, using it to devise visualisation methods and a wide variety of solvers for flutter problems. We assess these solvers, applying them to real-life aeroelastic systems and measuring their performance. We then discuss and devise methods for improving these solvers. All our conclusions are supported by a variety of evidence from numerical experiments. Finally, we assess all of our methods, providing recommendations as to their use and future development.
We do achieve several things in this thesis which have not been achieved before. Firstly, we solved a non-trivial flutter problem with a direct solver. The only direct solvers that have previously been presented are those that arise from classical flutter analysis, which applies only to very simple systems. Secondly, and as an extension of this first point, we solved a system with Theodorsen aerodynamics (approximated by a highly accurately) with a direct solver. This was achieved in an industrially competitive time (0.2s). This has never before been achieved. Thirdly, we solved an unstructured multiparameter eigenvalue problem. Unstructured problems have not been considered before, even in theoretical literature. This result is thus of significance both for multiparameter spectral theory and aeroelasticity. However, the single most important contribution of this thesis is the opening of a whole new field of study which stretches beyond aeroelasticity and into other industries: the treatment of instability problems using multiparameter methods. This field of research is wide and untrodden, and has the potential to change the way we analyse instability across many industries.
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Jagiello, Jakub. "PERFORMANCE COMPARISON BETWEEN REACT NATIVE AND FLUTTER." Thesis, Umeå universitet, Institutionen för datavetenskap, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-163190.
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The global mobile OS market share is mainly dominated by two operative systems. One of them is Android, and the other one called iOS. These two together had more than 99% of the market share in 2018, and it does not look like this trend is going to change anytime soon. Because of these two completely different platforms, there are many frameworks that provide solutions for developing applications that are platform independent. This study contains performance comparison between two of the more popular frameworks called Fluer and React Native. The performance is measured in terms of the number of dropped frames under a certain time for two different applications. The results that were acquired during tests reveal that React Native dropped less frames in total, although the difference was not significant.
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Li, Rui. "NUMERICAL INVESTIGATION OF THE INFLUENCE OF FRONT CAMBER ON THE STABILITY OF A COMPRESSOR AIRFOIL." UKnowledge, 2005. http://uknowledge.uky.edu/gradschool_theses/345.
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With the advent of smart materials it is becoming possible to alter the structural characteristics of turbomachine airfoils. This change in structural characteristics can include, but is not limited to, changes in the shape (morphing) of the airfoil. Through changes in the airfoil shape, aerodynamic performance can be improved. Moreover, this technique has the potential to act as a flutter suppressant. In this investigation changes in the airfoil front camber while maintaining the airfoil thickness distribution are made to increase airfoil stability. The airfoil section is representative of current low aspect ratio fan blade tip sections. To assess the influence of the change in airfoil shape on stability the work-per-cycle was evaluated for torsion mode oscillations around the mid-chord at an inlet Mach number of 0.5 with an interblade phase angle of 180 degree Cchordal incidence angles of both 0 degree and 10 degree, and a reduced frequency of 0.4.
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McHugh, Garrett R. "An Experimental Investigation in the Mitigation of Flutter Oscillation Using Shape Memory Alloys." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1479119992818089.
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Scucchia, Matteo. "Flutter: la nuova frontiera delle app platform-independent." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18459/.
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Il termine "platform-independent" in informatica si riferisce a linguaggi di programmazione, applicazioni software o dispositivi hardware che funzionano su differenti sistemi operativi e quindi su più piattaforme. Le app platform-independent, anche denominate cross-platform, sono applicazioni mobile che non necessitano di
differenti codifiche per essere operative su diversi sistemi. La tesi è incentrata sul framework Flutter, utilizzato per lo sviluppo della parte progettuale, che permette di scrivere un unico codice in linguaggio Dart e renderlo funzionante sia in ambiente Android che in ambiente iOS. Il mercato delle app mobile si sta espandendo esponenzialmente e sempre più spesso sono ricercate soluzioni che ne semplifichino lo sviluppo. Flutter è un progetto nato proprio per questo in quanto mette a disposizione Dart, un linguaggio molto semplice e intuitivo, ma al contempo estremamente potente, e astrazioni di Google già collaudate come la libreria Material che consentono la creazione in tempi rapidi di applicazioni fluide e ottimizzate. Nella tesi viene presentato Active CRM, un caso di studio realizzato con questa tecnologia che permette di gestire il modulo CRM di una azienda, pianificando attività e indirizzando i clienti negli acquisti.
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Yildiz, Erdinc Nuri. "Aeroelastic Stability Prediction Using Flutter Flight Test Data." Phd thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608623/index.pdf.
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Flutter analyses and tests are the major items in flight certification efforts required when a new air vehicle is developed or when a new external store is developed for an existing aircraft. The flight envelope of a new aircraft as well as the influence of aircraft modifications on an existing flight envelope can be safely determined only by flutter tests. In such tests, the aircraft is instrumented by accelerometers and exciters. Vibrations of the aircraft at specific dynamic pressures are measured and transmitted to a ground station via telemetry systems during flutter tests. These vibration data are analyzed online by using a flutter test software with various methods implemented in order to predict the safety margin with respect to flutter. Tests are performed at incrementally increasing dynamic pressures and safety regions of the flight envelope are determined step by step. Since flutter is a very destructive instability, tests are performed without getting too close to the flutter speed and estimations are performed by extrapolation.
In this study, pretest analyses and flutter prediction methods that can be used in various flight conditions are investigated. Existing methods are improved and their applications are demonstrated with experiments. A novel method to predict limit
cycle oscillations that are encountered in some modern fighter aircraft is developed. The prediction method developed in this study can effectively be used in cases where the nonlinearities in aircraft dynamics and air flow reduce the applicability of the
classical prediction methods. Some further methods to reduce the adverse effects of these nonlinearities on the predictions are also developed.
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Jinghe, Ren. "Development of a Shrouded SteamTurbine Flutter Test Case." Thesis, KTH, Kraft- och värmeteknologi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-225857.
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A shrouded blade was designed as a test case for flutter analysis of steam turbine. Flutter is a self-excitedvibration. It can lead to dramatic blade loss and high-cycle fatigue. Shrouded blade is more complicated onflutter analysis, because the mode shapes are more complex with bending and torsion components atdifferent phases. Moreover, the blade mode shape and frequency also vary with nodal diameter. Lack ofopen resource of shrouded blade, there were less researches about shrouded blade test case on flutter. The initial blade geometry was from Di Qi’s 3D free standing blade test case. The material of the blade isTitanium. The aim of current study is to design a 3D test case for realistic shrouded blade flutter analysis. The geometryof the proposed shrouded blade test case was fully described in this thesis report. ANSYS ICEM was usedfor presenting the geometry and generating mesh. ANSYS APDL was used for structural analysis.Parameters of shroud parts were based on literature reviews and engineers’ general suggestions. The modeshapes for the first family of modes were calculated and reported.Ett höljeblad utformades som ett testfall för fladderanalys av ångturbin. Flutter är en självupphetsadvibration. Det kan leda till dramatisk bladförlust och högcykelutmattning. Höljeblad är mer kompliceratvid fladderanalys, eftersom modeformerna är mer komplexa med böjnings- och torsionskomponenter iolika faser. Dessutom varierar bladformsformen och frekvensen också med noddiameter. Brist på öppenresurs av höljet blad, det fanns mindre undersökningar om höljet blad test fall på flutter. Den ursprungligabladgeometrin var från Di Qis 3D frittstående bladprovfall. Bladets material är titan. Syftet med den aktuella studien är att designa ett 3D-testfall för realistisk hävd bladflöjtsanalys. Geometrinhos det föreslagna höljet av bladsprov beskrivs fullständigt i denna avhandlingsrapport. ANSYS ICEManvändes för att presentera geometrin och det genererande nätet. ANSYS APDL användes för strukturellanalys. Parametrar av höljesdelar baserades på litteraturrecensioner och ingenjörers allmänna förslag.Modeshistorierna för den första familjen av lägen beräknades och rapporterades.
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Li, Wei. "Atrial flutter in grown up congenital heart patients." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251859.
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Milandre, Olivier. "Numerical modeling of flutter in a transonic fan." Thesis, KTH, Flygdynamik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-159276.
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Flutter is a self-feeding and potentially destructive vibration that can lead to devastating effects such as broken blades. Using accurate numerical models to predict flutter in the conception of an engine is essential to avoid huge waste of money. The software 2, using the elsA CFD package developed by the French Aerospace Lab, ONERA, is used to perform unsteady calculations and predict flutter margin. The current methodology does not systematically manage to reproduce the expected flutter pocket in transonic areas. The aim of the study is to investigate the impact of some parameters, such as boundary conditions and the position of the inlet and outlet plans of the mesh, on unsteady results. Results show that the current methodology, using conditions of injection at the inlet and an association of radial equilibrium and valve law boundary at the outlet, is inaccurate due to problem of reflecting waves that disturb the results. Using conditions of non-reflection at the inlet and the outlet seems more appropriate. Nevertheless, the new flutter margin using conditions of non-reflection does not permit to reproduce the flutter pocket either. New lines of investigation such as the impact of the density of the mesh or the time scheme may improve the numerical results.
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Gondoly, Karen Denise. "Application of advanced robustness analysis to experimental flutter." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/47383.
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PENNACHIONI, M. "ROTATING AERODYNAMIC- EXCITERS for in-flight flutter testing." International Foundation for Telemetering, 1985. http://hdl.handle.net/10150/615759.
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International Telemetering Conference Proceedings / October 28-31, 1985 / Riviera Hotel, Las Vegas, NevadaTelemetering, as used in in-flight testing, has several advantages including that of allowing what is known as real-time utilization; and thereby, in certain specific cases, the continuation of the flight programme in terms of the results obtained therein. This feature is especially attractive during the opening of the aircraft’s flutter envelope. It then becomes a matter of experimentally determining the aircraft’s aeroelastic stability throughout its flight envelope, and specifically at high speeds. In this connection, it’s common knowledge that in excess of a certain so-called critical speed, two or more vibratory modes of the structure can become coupled via the aerodynamic forces they respectively generate; and can lead to diverging oscillation liable to cause vibration failure. It’s easy to see that such a critical speed must be well within the permitted aircraft operation envelope and that approaching it during in-flight testing should only be considered with a certain amount of prudence and subject to strict monitoring of the structure’s behaviour. The most widely used monitoring system is to measure the transfer function relating an alternating force applied to the aircraft structure in flight to the displacements it causes at different points of that structure (figure 1). Progress in the flight envelope is made in speed steps, any variations in this transfer function being monitored between steps, and usually being reflected in terms of vibration frequencies and damping. Using telemetering, as in conducting these tests, is beneficial in several respects (figure 2). First it allows instant visual monitoring of the structure’s behaviour at its most significant points (rudders, bearing surface ends) by a team conveniently arranged on the ground. Then, further to a preliminary processing operation occurring in real-time, the test can be validated by merely observing the spectrums and the coherence functions existing between the forces applied and the structure’s response; a poor quality test, either due to a mismatched excitation or to the unexpected effect of an atmospheric turbulence, can be rerun without waiting for the aircraft to land. Finally, if adequate computing facilities are available, a comprehensive utilization of the values measured and their identification with a theoretical model lets the structure’s general behaviour be compared with the estimated figures, and thereby lets the aircraft resume the same test sequence at a higher speed or Mach number. The accuracy of the result and the speed at which it is obtained, so essential to the safe resumption of the flight, primarily depend on the extent and on the adequacy of the available information on the artificially applied forces. The design of “exciters” capable of creating controlled and measurable forces of an adequate level is thus the most vital constraint of the flutter testing facility.
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Rocha, José Celso. "Um controlador de flutter baseado em lógica difusa." Universidade de São Paulo, 2003. http://www.teses.usp.br/teses/disponiveis/18/18135/tde-01022016-165106/.
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O controle de flutter é um problema cuja solução é almejada ao longo de décadas e que ainda se apresenta como um desafio considerável. Os desafios residem basicamente no projeto de dispositivos de atuação eficientes e na síntese das leis de controle. A lógica difusa se mostra como uma técnica promissora e efetiva de controle. Neste trabalho é proposto um controlador difuso para o controle de flutter em uma asa com aerofólio do tipo NACA 0012, tendo como superfície de controle um flap. Este modelo físico é acoplado a um dispositivo elástico de sustentação da asa - DESA, que possibilita os movimentos de arfagem e deslocamento vertical. Para o desenvolvimento do modelo matemático são utilizadas as Equações de Lagrange e o Princípio do Trabalho Virtual. A determinação dos parâmetros estruturais do conjunto ASA/DESA é realizada a partir de um modelo em elementos finitos e de uma análise modal experimental. Os modos de vibrar são determinados através do ERA - Eigensystem Realization Algorithm. O estudo da atuação do controlador difuso é realizado através de simulação computacional e de análise experimental. Dois modelos difusos são utilizados na construção do controlador, o de Mamdani e o de Takagi-Sugeno-Kang. Os resultados obtidos mostram que o controlador difuso, para os dois modelos, é bastante eficiente no controle do flutter.Flutter control is a problem for which solution has been longed for decades and still is a considerable challenge. The challenges reside basically in the development of devices with efficient performance and in the synthesis of the control laws. Fuzzy logic appears as a promising and effective technique of control. In this work, a fuzzy controller is proposed for flutter control of a wing with NACA 0012 airfoil section, having as control surface a trailing edge flap. This physical model is coupled to the elastic support device of the wing - DESA, which allows plunge and pitch displacements. For the development of the mathematical modeI, the Lagrange Equations and the Principle of the Virtual Work are used. The determination of the structural parameters of the Wing/DESA device is accomplished starting from a finite element model and from an experimental modal analysis. The vibrating modes are obtained using the Eigensystem Realization AIgorithm - ERA. The study of the fuzzy controllers performance is accomplished through simulation and experimental analysis. Two fuzzy models are used for the controller: the Mamdani and the Takagi- Sugeno-Kang. The results show that both fuzzy controllers are quite efficient in the control of flutter.
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Da, Costa Antoine. "Le flutter auriculaire : évolution du traitement par radiofréquence." Saint-Etienne, 2003. http://www.theses.fr/2003STET014T.
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Notre travail avait trois axes essentiels, le premier concernait la prise en charge thérapeutique après radiofréquence en évaluant les facteurs prédictifs de survenue de fibrillation auriculaire, le deuxième était une évaluation du traitement par radiofréquence chez le sujet âgé et le troisième l'évaluation de l'impact du choix du cathéter en fonction de l'anatomie de l'oreillette droite sur la durée et le succès des procédures d'ablation. Notre premier travail, a montré en analyse multivariée que la présence d'une dysfonction ventriculaire gauche, des antécédents de fibrillation auriculaire ou la présence d'une valvulopathie mitrale étaient des facteurs prédictifs indépendants de fibrillation auriculaire au décours d'une ablation par radiofréquence de flutter auriculaire. La seconde partie de notre travail a montré la faisabilité et l'innocuité du traitement par radiofréquence chez des patients avec flutter auriculaire dans une population âgée par rapport des sujets plus jeunes. Notre troisième travail prospectif randomisé a comparé deux types de cathéters (cathéter non irrigué 8 mm et cathéter irrigué 5 mm) avec haut niveau d'efficacité dans cette indication, mais aussi l'influence de l'anatomie sur les procédures d'ablation. Notre étude n'a pas montré de différence d'efficacité entre ces deux types de cathéters dans le groupe de patients réputé le plus difficile car présentant un isthme cavo-tricuspide long. Nous montrons que ce sont des différences anatomiques qui ont une influence directe sur la durée des procédures ablatives.
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Pasquié, Jean-Luc. "Ablation du flutter auriculaire par courant de radiofréquence." Montpellier 1, 1995. http://www.theses.fr/1995MON11055.
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Cyteval, Georges Alain. "Electro-physiologie clinique dans le flutter auriculaire commun." Montpellier 1, 1989. http://www.theses.fr/1989MON11241.
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Stender, Simon, and Hampus Åkesson. "Cross-platform Framework Comparison : Flutter & React Native." Thesis, Blekinge Tekniska Högskola, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-19749.
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The development of apps in a cross-platform framework is something that has been appearing more over the latest years. But the knowledge of knowing which of the two popular frameworks, React Native, and Flutter are most efficient when it comes to resource management and general comparisons are less known. This is what this thesis investigates. To find out the comparisons between React Native and Flutter we created two similar apps and document the process of creating an app with the selected frameworks. To get data on the differences when developing an app with these frameworks, we made a survey to get more experienced developers' input. We then did performance tests of the apps to be able to compare the results of the respective framework. The applications we built had several similar functionalities that we used to measure the performance. We also touched on the subject of comparison between a cross-platform framework and a native framework. To do this we performed a literature review on related work to conclude the approaches. From our result, we could conclude that the performance of the Flutter app had a slight advantage over the React Native app. But the difference was not that remarkable, and the overall development was fairly similar. There were some differences to the approaches of development when it came to less experienced developers compared to more experienced developers which we learn from our survey. More experienced developers tended to use external debugging tools, while less experienced used built-in tools such as console commands. Finally, we want to conclude that both Flutter and React Native has their pros and cons. Both frameworks have a big community which is growing everyday, but we believe that Flutter might overtake the popularity from React Native due to its slight performance superiority.From our literature review we can conclude that both approaches has their advantages and it depends a lot on the concept of the app. When developing a more complex app, the native approach is superior. When developing smaller apps with shorter life periods, cross-platform will faster get the app on the market.
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Seresta, Omprakash. "Buckling, Flutter, and Postbuckling Optimization of Composite Structures." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/26401.
Full textAbstract:
This research work deals with the design and optimization of a large composite structure. In
design of large structural systems, it is customary to divide the problem into many smaller
independent/semi-independent local design problems. For example, the wing structure design
problem is decomposed into several local panel design problem. The use of composite
necessitates the inclusion of ply angles as design variables. These design variables are discrete
in nature because of manufacturing constraint. The multilevel approach results into
a nonblended solution with no continuity of laminate layups across the panels. The nonblended
solution is not desirable because of two reasons. First, the structural integrity of
the whole system is questionable. Second, even if there is continuity to some extent, the
manufacturing process ends up being costlier.
In this work, we develop a global local design methodology to design blended composite
laminates across the whole structural system. The blending constraint is imposed via a guide
based approach within the genetic algorithm optimization scheme. Two different blending
schemes are investigated, outer and inner blending. The global local approach is implemented
for a complex composite wing structure design problem, which is known to have a strong
global local coupling. To reduce the computational cost, the originally proposed local one
dimensional search is replaced by an intuitive local improvement operator. The local panels
design problem arises in global/local wing structure design has a straight edge boundary
condition. A postbuckling analysis module is developed for such panels with applied edge
displacements. A parametric study of the effects of flexural and inplane stiffnesses on the
design of composite laminates for optimal postbuckling performance is done. The design
optimization of composite laminates for postbuckling strength is properly formulated with
stacking sequence as design variables.
Next, we formulate the stacking sequence design (fiber orientation angle of the layers) of
laminated composite flat panels for maximum supersonic flutter speed and maximum thermal
buckling capacity. The design is constrained so that the behavior of the panel in the vicinity
of the flutter boundary should be limited to stable limit cycle oscillation. A parametric study
is carried out to investigate the tradeoff between designs for thermal buckling and flutter.
In an effort to include the postbuckling constraint into the multilevel design optimization
of large composite structure, an alternative cheap methodology for predicting load paths
in postbuckled structure is presented. This approach being computationally less expensive
compared to full scale nonlinear analysis can be used in conjunction with an optimizer for
preliminary design of large composite structure with postbuckling constraint. This approach
assumes that the postbuckled stiffness of the structure, though reduced considerably, remains
linear. The analytical expressions for postbuckled stiffness are given in a form that can
be used with any commercially available linear finite element solver. Using the developed
approximate load path prediction scheme, a global local design approach is developed to
design large composite structure with blending and local postbuckling constraints. The
methodology is demonstrated via a composite wing box design with blended laminates.Ph. D.
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Björemo, Christine. "En kvalitativ studie om Flutter : Apputveckling inom crossplattform." Thesis, Karlstads universitet, Handelshögskolan (from 2013), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-80688.
Full textAbstract:
Syftet med denna kandidatuppsats i informatik är att undersöka på vilket sätt ramverket Flutter underlättar för dagens apputvecklare i cross-plattformmiljöer. Uppsatsen belyser för- och nackdelar med Flutter utifrån apputvecklare-perspektiv. Det största problemområde från tidigare studier och forskningar inom cross-plattformutveckling är främst den undermåttliga dokumentation samt långa utvecklingstider. Denna kvalitativa studie är fokuserad på dessa problemområden och resultatet presenteras under kapitel 4 ”Resultat”. En analysmodell har utformats och använts i syfte att, för respondenter, svara på relevanta frågor där ramverket Flutter hanterar dessa viktiga problemområden. Slutsatsen av denna studie visar att det finns ett tydligt mönster där ramverktyget Flutter har satsat på att hantera dessa problemområden genom följande styrkor: Verktyget ”Hot Reload” (hjälpmedel som uppdaterar koden för att snabbt se ändringar direkt i simulatorn) Dart (ett programmeringsspråk) Dokumentation (tydlig, alltid i tid och flera olika kommunikationskanaler) Parallellt med kandidatuppsatsen har författaren utvecklat en egen app via Flutter. Syftet med denna app är att underlätta semesterplaneringen åt en avdelning på företaget AFRY. I denna kandidatuppstats används ej författarens egna upplevelser med Flutter som empiri men avslutar uppsatsen med egna reflektioner.
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Dahl, Ola. "Exploring End User’s Perception of Flutter Mobile Apps." Thesis, Malmö universitet, Fakulteten för teknik och samhälle (TS), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:mau:diva-20519.
Full textAbstract:
Vid utveckling av mobila applikationer måste utvecklare göra ett val: antingen utvecklaflera nativa applikationer för olika operativsystem eller utveckla en applikation som kanköras på flera plattformar. Många teknologier för att skapa plattformsoberoende applikationer har uppstått genom åren, och nya teknologier släpps varje år. En sådan teknologi är Flutter, som är ett SDK (Software Development Kit) för mobila applikationer. Flutter lovar möjligheten att bygga nativa applikationer för iOS och Android som har nativprestanda.För att svara på om detta påstående är sant, från en användares perspektiv, utveckladestvå visuellt identiska mobila applikationer. En applikation utvecklades med Flutters SDKoch en med Androids nativa SDK. Applikationerna utvärderades därefter av användaresom svarade på hur deras upplevelse var av att använda applikationerna. Användarnasvarade också ifall de föredrog någon av applikationerna.Resultatet visar att det finns en skillnad mellan applikationerna i användarnas upplevelseav hastighet, men inte i deras upplevelse av utseende. Användarna upplevde atthastigheten var snabbare hos den nativa applikationen jämfört med Flutter-applikationen,men upplevde utseendet av applikationerna som lika. En majoritet av användarna sa att de föredrog den nativa applikationen och endast 10% sa att de föredrog Flutter-applikationen.When developing mobile applications, developers need to make a decition: either developmultiple native applications for different operating systems or developing one app thatis cross-platform compatible. Many technologies for creating cross-platform applicationshave emerged over the years, and new techologies are released every year. One suchtechnology is Flutter, which is a mobile application SDK (Software Development Kit).Flutter promises the ability to build native applications on iOS and Android that achievenative performance.To answer if this statement is true, from a user’s perspective, two visually identicalmobile applications were developed. One application was developed using the FlutterSDK and one using the native Android SDK. The applications were then evaluated byusers who were asked about their perception of using the applications. Users were alsoasked if they preferred any of the applications.The result show a clear difference between the applications in user’s perception of speed,but not in their perception of appearance. Users perceived the speed of the native application to be faster than the speed of the Flutter application, but perceived the apperance of both applications to be equal. A majority of users said that they preferred the native application and only 10% said that they preferred the Flutter application.
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Wheeler, Philip Curtis. "An explication of airfoil section bending-torsion flutter." College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/1375.
Full textAbstract:
Thesis (M.S.) -- University of Maryland, College Park, 2004.Thesis research directed by: Dept. of Civil and Environmental Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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An, Sui. "Aeroelastic design of a lightweight distributed electric propulsion aircraft with flutter and strength requirements." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53593.
Full textAbstract:
Distributed electric propulsion is a promising technology currently being considered for gen- eral aviation-class aircraft that has the potential to increase range and performance without sacrificing low-speed flight characteristics. However, the high-aspect ratio wings enabled by distributed electric propulsion make these designs more susceptible to adverse aeroe- lastic phenomena. This thesis describes the development of a gradient-based optimization framework for aircraft with distributed electric propulsion using structural and aeroelastic constraints. The governing equations for the coupled aeroelastic system form the basis of the static aeroelastic and flutter analysis. In this work, the Doublet-Lattice method is used to evaluate the aerodynamic forces exerted on the wing surface. In order to consider the impact of propeller-induced flow on aerodynamic loading, a one-way propeller-wing coupling is com- puted by superposition of the propeller induced velocity profile calculated using actuator disk theory and the wing flow field. The structural finite-element analysis is performed using the Toolkit for the Analysis of Composite Structures (TACS). The infinite-plate spline method is used to perform load and displacement transfer between the aerodynamic surface and the structural model. Instead of utilizing a conventional flutter analysis, the Jacobi-Davidson method is used to solve the governing eigenvalue problem without a reduction to the lowest structural modes, facilitating the evaluation of the gradient for design optimization. This framework is applied to different configurations with distributed electric propulsion to minimize structural weight subject to structural and aeroelastic constraints. The effect of flutter constraints, wing aspect ratio, and electric propeller quantity are compared through a series of design optimization studies. The results show that larger aspect ratio wings and more electric motors lead to heavier wings that are more susceptible to flutter. This framework can be used to develop lighter aircraft with distributed electric propulsion configuration that satisfy strength and flutter requirements.
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Hayden, Andrew Phillip. "Initial Investigations into the Failure Modes of a Swirl Distortion Generator Using Computational Methods." Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/103375.
Full textAbstract:
The need for more efficient and environmentally sustainable aircraft has been a rapidly increasing topic for research and development over the last few decades. Within this area of research, boundary layer ingestion (BLI) concepts have been developed which integrates the airframe and propulsion system of an aircraft. In turn, BLI increases the fuel efficiency and decreases emissions by reducing the overall drag and reenergizing the aircraft wake. However, the boundary layer flow of an airframe or duct can impose undesired flow conditions, such as swirl and pressure distortions, at the inlet of a jet engine. Therefore, efficient research and testing capabilities are essential to advance the development of these integrated systems.
The StreamVane swirl distortion generator was developed by Virginia Tech to provide cost and time efficient ground testing methods for BLI research. StreamVanes are constructed of unique vane packs that are specifically tailored to generate a desired swirl distortion profile. To maximize efficiency, StreamVanes are additive manufactured which cause geometry limitations to the overall vane design. Due to these restrictions, as well as the complexity of the vane pack, unwanted dynamic responses and unsteady flows can be generated. In order to predict both of these phenomena before testing, two different computational methodologies were developed and investigated on a StreamVane and its airfoil parameters.
First, a one-way fluid-structure interaction methodology was developed to predict flutter mconditions of the vanes within StreamVanes. The presented methodology includes steady and unsteady computational fluid dynamics (CFD) as well as linear structural and modal finite element analysis (FEA) simulations. A simplified StreamVane model was designed as a testcase for the methodology, and it was found that two unique vane shapes did not undergo flutter conditions at three different operating points. The results provided a linear analysis method to compute the aerodynamic damping, which gave insight on how different vane shapes respond dynamically.
Secondly, a parameter study was conducted to predict the vortex shedding from the modified NACA 63-series airfoil profile used within StreamVane design. The effects of the airfoil turning angle and trailing edge thickness on the vortex shedding frequency were computationally predicted using the unsteady Reynolds averaged Navier-Stokes equations (URANS) and shear stress transport (SST) turbulence model. In turn, the shedding frequencies for each parameter were recorded, and more intuition was gained on the TE flow field in correspondence to different airfoil specifications. Overall, the two sets of methodologies and results can be used to efficiently reduce failure uncertainties in future StreamVane designs.Master of Science
The need for more efficient and environmentally sustainable aircraft has been a rapidly increasing topic for research and development over the last few decades. Within this area of research, boundary layer ingestion (BLI) concepts have been developed to advance the fuel efficiency in future aircraft designs. However, unlike traditional tube and wing aircraft, BLI produces nonuniform flow at the engine inlet, reducing the performance and durability of jet engine components. Therefore, more efficient research and testing capabilities are essential to advance the development of BLI aircraft. The StreamVane swirl distortion generator was developed by Virginia Tech to provide cost and time efficient ground testing methods for BLI research. These devices can be secured upstream of a test engine, and their complex vane pack can produce the same nonuniform flow found at the inlet of BLI aircraft engines. To further increase efficiency, StreamVanes are additive manufactured which causes geometry limitations to the overall vane design. Due to these restrictions, as well as the complexity of the vane pack, unwanted dynamic responses and unsteady flows can be generated. In order to predict both of these phenomena before testing, two different computational methodologies were developed and investigated on a StreamVane and its airfoil parameters. The first methodology was developed to compute the fluid dynamics and structural response of a simplified StreamVane model at different operating conditions. The results provided insight on how different vanes react dynamically to the surrounding flow field. The second methodology included a parameter study to predict the frequencies generated from the StreamVane airfoils. With these frequencies, more intuition was gained on how the overall fluid-structure system would behave. Overall, both methodologies and results can be used to efficiently reduce failure uncertainties in future StreamVane designs.
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Olsson, Matilda. "A Comparison of Performance and Looks Between Flutter and Native Applications : When to prefer Flutter over native in mobile application development." Thesis, Blekinge Tekniska Högskola, Institutionen för programvaruteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-19712.
Full textAbstract:
A mobile application has to be able to keep up with heavy demands to compete with all the new applications that are developed each day. Good performance and nice visuals are base requirements for the development of mobile applications. There are many options for tools when developing and one of these choices is a native application, which is said to have better performance and suitability to the mobile environment. Another choice is a tool which requires only one code base for multiple platforms and is therefore easier to maintain. Flutter is an open-source User Interface (UI) toolkit created by Google that can create cross-platform applications with one code base while said to maintain the aspects of looking native. This paper explores how Flutter compares to native applications, which are currently seen as superior in mobile behaviour and performance. An experiment was conducted to test how Flutter as a cross-compiler compared to two native applications made of kotlin and Android studio and swift and XCode, in terms of CPU performance. A survey was created to see if there was a difference in the perception of users with regards to appearance and animations. A literature study was conducted to strengthen the results from the experiment and survey and to give a background to the subject. Flutter is a new tool and it continues to grow incredibly fast. Conclusions are drawn that a Flutter application can compete with a native application when it comes to CPU performance, but is not as developed in the animation area. Flutter does not require complex code for creating a simple application and uses significantly less lines of code in development compared to native. The final conclusion is that Flutter is best to use when building smaller to medium-sized applications, but has a potential to grow to overcome its current drawbacks in the animation department. Further examination of the areas examined in this paper is needed in order to ensure and strengthen the results.